Barack Obama is to send thousands of campaign volunteers across the US this weekend as part of an urgent effort to create one of the most sophisticated political operations ever to contest a White House election.

Although there are still 143 days left before the election, Obama is moving at speed to establish an operation he hopes will out-organise his Republican rival John McCain in the swing states.

Around 3,600 volunteers are being dispatched to reinforce advance staff deployed in 17 states. Although he has said he will fight all 50 states, his campaign has identified these as ones that could determine the outcome of the November 4 general election.

The mobilisation comes as Obama and McCain engaged in a dispute over a proposal by the Republican candidate for the two to hold 10 town hall debates between now and the first of the party conventions in August.

McCain, who is at his best in smaller gatherings, expressed disappointment that Obama had failed to take up his offer. But Obama's campaign chief, David Plouffe, fired back that Obama had agreed, though only to two such events - one in July and one in August.

Plouffe said these two, combined with the traditional three television debates in the autumn, would be "the most of any presidential campaign in the modern era".

He added: "It's disappointing that senator McCain and his campaign decided to decline this proposal. Apparently they would rather contrive a political issue than foster a genuine discussion about the future of our country."

Obama's 3,600 volunteers have given a commitment to do at least six weeks of unpaid political work. He put out a call for volunteers in April and more than 10,000 replied.

Obama established a formidable reputation in his battle with Hillary Clinton for grassroots organisation, pinpointing potential voters in places such as Iowa on a scale never before seen in American politics.

He wants to replicate that in the general election, not only in Iowa but into swing states such as Ohio, Pennsylvania, Florida, Virginia, Colorado, Nevada and New Mexico.

McCain, though he wrapped up the Republican nomination in March, has struggled to develop a Republican general election machine on the ground in states such as Ohio, in part because of a reluctance of rightwing activists to work for him.

By contrast, Obama, though he won the Democratic nomination only last week, has shifted quickly into general election mode.

Reflecting this, he is to move large parts of the Democratic headquarters staff from Washington to his campaign headquarters in his home town, Chicago.

A spokesman for the Democratic national committee, Stacie Paxton, declined yesterday to give details of the move but said: "The DNC and the Obama campaign are going to be one seamless, integrated operation. The idea is not to duplicate efforts."

Staff from the party's political, field and constituency operations will be moved to Chicago or to help out in key states.

Obama wants to try to avoid the kind of unnecessary duplication that hampered John Kerry's failed 2004 bid for the White House, when he won 251 electoral college votes, 19 short of the 270 needed to beat George Bush.

His aim is to keep the 19 states that Kerry won and add at least a few of the swing states. He spent yesterday in one of them, Ohio, where he promised to reform social security, and is due today to speak in another, Pennsylvania.

As well as good on-the-ground organisation, one of the reasons for Obama's success so far has been that he has made better use of the internet than his rivals.

Joe Rospars, who is the head of new media for Obama, speaking at a conference in Washington this week, said that the internet had helped the campaign build a network of one million supporters across the US and 1.5 million donors, most of them providing $200 (£100) or less.

Joe Trippi, who was among the first political operators to harness the internet on behalf of the failed Democratic candidate Howard Dean in 2004, was due to speak at the conference but, unable to attend, had his comments read out, including a prediction that Obama would raise half a billion dollars by November.

The latest opinion poll, published by NBC and the Wall Street Journal on Wednesday, puts Obama on 47% and McCain on 41%.